1. Signaling System #7 Kamalasanan.PK
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MSC Ernakulam

2. Types of Signaling Signaling in Telecommunications Network
Channel Associated Signaling (CAS)
Common Channel Signaling (CCS)
Signaling System Number (SS7) is a form of Common Channel Signaling.
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MSC Ernakulam

3. Common Channel Signaling
Out of Band signaling
Employs separate, dedicated path for signaling.
Voice trunks are used only when a connection is established, not before.
Faster Call Setup.
Switch A B
Voice Trunks
Signaling Link
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MSC Ernakulam

4. Advantage of CCS over CAS
Faster call setup
No interference between signaling tones by network and frequency of human speech pattern.
Greater Trunking Efficiency:- CCS has shorter call set up time that result in less call holding time, thereby reducing the traffic on the network.
Information Transfer:- CCS allows the transfer of additional information along with the signaling traffic providing facilities such as caller identification and voice or data identification
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MSC Ernakulam

5. SS7 Principle Out of band Signaling
Higher Signaling data rates (56Kbps & 64 Kbps) for LSL and 2Mbps for HSL
Signaling traffic is bursty and of short duration, hence operates in connectionless mode using packet switching
Variable length signal units with maximum size limitation
Optimum use of bandwidth
Reliability and flexibility
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MSC Ernakulam

6. Definition
SS7 or Signaling System Number 7 is a set of protocols that describes a means of communication between telephone switches in public telephone networks. SS7 is a highly sophisticated and powerful form of Common Channel Signaling (CCS). The use of out-of-band signaling procedures offers considerable benefits over and above other signaling methodologies.
SS7 is a layered system, in which each layer (level)
contains a well-defined functionality, including the
interface (functions and procedures).
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7. SS7 Networks
STP
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MSC Ernakulam

8. Service switching point (SSP)
SSPs are switches that have SS7 software and terminating signaling links
SSPs create packets (signal units) and send those messages to other SSPs, as well as queries to remote shared databases to find out how to route calls
SSPs communicate with the voice switch via the use of primitives and have the ability to send messages using ISUP (call setup and teardown) and TCAP (database lookup) protocols.
The switch can originate, terminate, or switch calls
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MSC Ernakulam

9. Signaling transfer point (STP)
STPs are packet switches, and act like routers in the SS7 network.
Routes each incoming message to an outgoing signaling link, based on routing information contained in the SS#7 message and a pre-defined route table
Does not offer termination services
STPs are paired to ensure redundancy
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MSC Ernakulam

10. Service control point (SCP)
An SCP is usually a computer used as a front end to a database system.
It is an interface to application-specific databases.
The address of an SCP is a point code, and the address of the database it interfaces with is a subsystem number.
The database is an application entity which is accessed via the TCAP protocol.
Databases that provides information necessary for advanced call processing capabilities
Accepts a query for information from a subsystem at another node
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MSC Ernakulam

11. SS7 Link Types
STP
STP
STP
STP
STP
STP
STP
STP
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MSC Ernakulam

12. SS7 Link Types A link (access)
Connects signaling end point (SCP or SSP) to STP.
B link (bridge)
Join mated STP pairs to other mated STP pairs of equal hierarchy and forms a quad structure.
C link (cross)
Connects STPs performing identical functions, forming a mated pair (for greater reliability). Provide alternate routing.
D link (diagonal)
Connects local and regional STP pairs.One level of STP pairs ,the secondary or local level,supports SSPs.
E link (extended)
Connects an CSP,SSP or signaling point to a remote STP pair to perform transaction services. (Note: E links are not recommended)
F link (fully associated)
Connects SCPs,SSPs and signaling points directly with one another.F links donot connect to STPs
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MSC Ernakulam

13. Common Channel Signaling Modes
There are three types of CCS signaling modes:
Associated
Quasi-associated
Non-associated
SS7 runs in associated or quasi-associated mode, but not in non-associated mode. Associated and quasi-associated signaling modes ensure sequential delivery, while non-associated does not. SS7 does not run in non-associated mode because it does not have procedures for reordering out-of-sequence messages.

14. Associated Signaling
both the signaling and the corresponding user traffic take the same route through the network.
Associated mode requires every network switch to have signaling links to every other interconnected switch (this is known as a fully meshed network design).

15. Quasi-Associated Signaling
In quasi-associated mode, signaling follows a different route than the switched traffic to which it refers, requiring the signaling to traverse at least one intermediate node. Quasi-associated networks tend to make better use of the signaling links.

16. LINK LINKSET PC = 1 PC = 2 ROUTE NODE A NODE B ROUTSET NODE C PC = 3
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MSC Ernakulam

17. LINK – Physical channel used for signaling.
LSL (Low Speed Link )- having a speed of 64Kbps
HSL (High Speed Link) – Having a speed of 2Mbps
LINKSET – Group of links between two nodes.
For LSL max of 16 links can be in a Linkset
For HSL max of 4 links can be in a Linkset
LINKSET GROUP – Group of Linkset in which priority has been given
ROUTE – Logical path between two nodes utilizing the linkset .
ROUTESET – Group of Routes two a specific destination.
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MSC Ernakulam

18. What goes over Signaling Link
Signaling information is passed over the signaling link in form of messages, which are called signaling units (SUs)
3 Types of SUs are:
Message signal units(MSUs)
Link status signal units(LSSUs)
Fill-in signal units(FISUs)
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MSC Ernakulam

19. Message signal unit (MSU)
Signaling Units
Message signal unit (MSU)
Carries signaling associated with call setup & database query and response and SS7 network input 1 1 1 1 1
8-272 1
FLAG
BSN/
BIB
FSN/
FIB
Length
Indicator
Service
Info. octet
Signaling
Info. field
Check
sum
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MSC Ernakulam

20. Signaling Units FLAG: Beginning of a new SU and is 01111110
BSN: Used to acknowledge receipt of SUs
BIB: Indicate the negative acknowledgement by the remote SP when toggled
FSN: Sequence number of the SU
FIB: Used in error recovery like BIB
SIO: Service Information Octet
SIF: Signaling Information Field
CRC: Cyclic Redundancy check
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MSC Ernakulam

21. Direction of transmission
Signaling Units Passing in Physical Layer
Format of Message Signal Unit (MSU) F CK
SIF
SIO S P A R E LI F I B
FSN B I
BSN F
Direction of transmission
Format of Link Status Signal Unit (LSSU) F CK SF S P A R E LI F I B
FSN B I
BSN F
Format of Fill-in Signal Unit (FISU) F CK S P A R E LI F I B
FSN B I
BSN F
F – Flag (8) SIF – Signaling Information Field (8n, n>2)
CK – Checksum (16) SIO – Service Information Octet (8)
LI – Length Indicator (6) FIB – Forward Indicator Bit (1)
FSN – Forward Sequence Number (7) BIB – Backward Indicator Bit (1)
BSN – Backward Sequence Number (7) SF – Status Field (8 or 16)
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MSC Ernakulam

22. LENGTH INDICATOR · LI = 0 indicates a FISU.
LI = 1 or 2 indicates an LSSU.
LI > 2 indicates a MSU
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MSC Ernakulam

23. Link status signaling units (LSSU)
Inform the far end about the changes in status of link
Message length can be 1 or 2 bytes
FLAG
BSN/
BIB
FSN/
FIB
Length
Indicator
Check
Sum 1
Status
Field
1 or 2
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MSC Ernakulam

24. Network Management (LSSU)
FORMAT..
USAGE OF CBA
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MSC Ernakulam

25. Fill-In Signal Units (FISU)
Signaling Units
Fill-In Signal Units (FISU)
Fill the gaps between MSU and LSSU messages
Sent only when the buffer is empty, to keep the signaling link active
Facilitate in constant monitoring of link quality.
FLAG
BSN/
BIB
FSN/
FIB
Length
Indicator
Check
Sum 1
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MSC Ernakulam

26. Message Signaling UnitF S P A R E
SIF B I LI CK
BSN
FSN
SIO 8 7 1 6 2
2-272 Bytes 16
279 Bytes
Q:How many MSU’s with fully loaded SIF’s will tranfer in One second?
Total Time required to transmit 1 MSU with 272 bytes SIF
1 bytes = 125 Micro second
One MSU = 279 X
= Seconds
1 Second = 28 MSU’s
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MSC Ernakulam

27. SS7 Protocol Stack
OSI
SS7
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MSC Ernakulam

28. Protocols Message Transfer Part (MTP Level 1) Physical
Provides an interface to the actual physical channel over which communication takes place
CCITT recommends 64Kbps transmission as LSL whereas ANSI recommends 56 Kbps
HSL provides a transmission speed of 2Mbps
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MSC Ernakulam

29. SS7 Protocol Overview
The SS7 physical layer is called MTP level 1 (MTP1)
The data link layer is called MTP level 2 (MTP2),
The network layer is called MTP level 3 (MTP3).
Collectively they are called the Message Transfer Part (MTP).
The MTP transfers the signaling message, in the correct sequence, without loss or duplication.
The MTP provides reliable transfer and delivery of signaling messages.

30. MTP2 MTP2 ensures reliable transfer of signaling messages.
It encapsulates signaling messages into variable-length SS7 packets.
SS7 packets are called signal units (SUs).
MTP2 provides delineation of SUs, alignment of SUs, signaling link error monitoring, error correction by retransmission, and flow control.
The MTP2 protocol is specific to narrowband links (56 or 64 kbps).

31. MTP3 MTP3 performs two functions:
Signaling Message Handling (SMH) Delivers incoming messages to their intended User Part and routes outgoing messages toward their destination. MTP3 uses the PC to identify the correct node for message delivery. Each message has both an Origination Point Code (OPC) and a DPC. The OPC is inserted into messages at the MTP3 level to identify the SP that originated the message. The DPC is inserted to identify the address of the destination SP. Routing tables within an SS7 node are used to route messages.
Signaling Network Management (SNM): Monitors linksets and routesets, providing status to network nodes so that traffic can be rerouted when necessary. SNM also provides procedures to take corrective action when failures occur, providing a self-healing mechanism for the SS7 network.

32. SCCP
SCCP provides a more flexible means of routing and provides mechanisms to transfer data over the SS7 network.
Such additional features are used to support non circuit-related signaling, which is mostly used to interact with databases (SCPs). It is also used to connect the radio related components in cellular networks and for inter-SSP communication supporting CLASS services.
For example, in cellular networks, SCCP transfers queries and responses between the Visitor Location Register (VLR) and Home Location Register (HLR) databases.

33. Format of SCCP message. - - > F CK SIF SIO LI FIB FSN BIB BSN F
Message Signal Unit
1st Bit Transmitted
- - > F CK
SIF
SIO LI
FIB
FSN
BIB
BSN F
SCCP
Message
Message
Type
MTP
Routing Label
SCCP Information
Mandatory
Variable
Part
Mandatory
Fixed Part
SLS
OPC
DPC
Optional Part
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MSC Ernakulam

34. Protocols Transaction Capabilities Applications Part (TCAP)
To establish more then one transaction between two ss7 nodes
Exchange of non-circuit related data
Between applications across the SS#7 network
Using the SCCP service
Queries and responses sent between Signaling Switching Point (SSPs) and Signaling Control Point (SCPs)
Sends and receives database information
Credit card validation
Routing information
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MSC Ernakulam

35. Transaction Portion Package Types
End
Ends a dialog between two nodes
Abort
Terminates the dialog abruptly without transmitting any pending component
Continue
Continues the dialog (for example, more messages can be sent)
Begin
Starts a dialog between two nodes
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MSC Ernakulam

36. Basic ERROR CORRECTION -With Error
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MSC Ernakulam

37. Service Information Octet (SIO)
In message signal units (MSUs), the service information
octet (SIO) is used to perform message distribution.
This octet is divided into a four-bit service indicator (SI)
and a four-bit subservice field. This subservice field is
further divided into a two-bit network-indicator code
and two bits that are spare if the indicator code is 00
or 01, or are available for national use if the indicator
code is 10 or 11.
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MSC Ernakulam

38. Sub-service field (4 bits) Service indicator (4 bits)
SIGNALLING NETWORK FUNCTIONS
Signaling Message Handling – SERVICE INFORMATION OCTET
D C B A
Sub-service field (4 bits)
Service indicator (4 bits)
Direction of transmission
Sub-service field = Network Indicator
(Bits A & B are spare)
Bit D
Bit C
Network Indicator 1
International Network
Not used
National network
Reserved for national use
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MSC Ernakulam

39. THANK YOU Kamalasanan
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MSC Ernakulam